Glucomannan and Diabetes

Glucomannan is a water-soluble dietary fiber that is derived from konjac root (Amorphophallus konjac). Like other forms of dietary fiber, it is considered a “bulk-forming laxative.” It promotes a larger, bulkier stool that passes through the colon more easily and requires less pressure—and subsequently less straining—to expel. Good results have been noted in preliminary and double-blind studies for the treatment of constipation. In constipated individuals, "bulk-forming laxatives" generally help produce a bowel movement within 12 to 24 hours. Its use for diverticular disease of the colon has also been studied in preliminary research; about one-third to one-half of the subjects were found to benefit from it.

It is a purified fiber from konjac root that is available as a bulk powder or in hard-gelatin capsules. Whether any foods contain significant amounts of it is unclear. As it is not an essential nutrient, no deficiency state exists.

What Can Glucomannan Do?

It can delay stomach emptying, leading to a more gradual absorption of dietary sugar; this effect can reduce the elevation of blood sugar levels that is typical after a meal. Controlled studies have found that after-meal blood sugar levels are lower in people with diabetes given it in their food, and overall diabetic control is improved with glucomannan-enriched diets according to preliminary and controlled trials. One preliminary report suggested that it may also be helpful in pregnancy-related diabetes. One double-blind study reported that it (8–13 grams per day) stabilized blood sugar in people with the insulin resistance syndrome (syndrome X). In a preliminary study, addition of either 2.6 or 5.2 grams of glucomannan to a meal prevented hypoglycemia in adults with previous stomach surgery; a similar study of children produced inconsistent results.

Like other soluble fibers, it can bind to bile acids in the gut and carry them out of the body in the feces, which requires the body to convert more cholesterol into bile acids. This can result in the lowering of blood cholesterol and other blood fats. Controlled and double-blind studies have shown that supplementation with several grams per day significantly reduced total blood cholesterol, LDL (“bad”) cholesterol, and triglycerides, and in some cases raised HDL (“good”) cholesterol. One double-blind study reported that it (8–13 grams per day) lowered total and LDL cholesterol in people with the insulin resistance syndrome.

It may help weight loss by occupying space in the stomach, thereby making a person feel full. One double-blind study reported weight loss averaging 5.5 pounds in adults when one gram of glucomannan was taken with a cup of water one hour before each meal for eight weeks. However, a similar study of overweight children found that it was not significantly more effective than a placebo. Other controlled studies have found that it improves the results of weight loss diets in overweight adults and children.

How Much is Usually Taken?

The amount shown to be effective as a laxative is 3–4 grams per day. Effective amounts for lowering blood cholesterol have been 4–13 grams per day. For controlling blood sugar, 500–700 mg per 100 calories in the diet has been used successfully in controlled research. For weight loss, 1 to 3 grams before each meal has been effective. When using it and other dietary fiber supplements, it is best to start out with a small amount and increase gradually. It is recommended to drink at least 8 ounces of water each time any bulk-forming laxative is taken.

Side Effects or Interactions

People with any disorder of the esophagus (the tube leading from the mouth to the stomach) should not take any fiber supplement in a pill form, as the supplement may expand in the esophagus and lead to obstruction. Preliminary reports in humans, as well and animal research, suggest that some people may be sensitive to inhaled glucomannan powder.
Since intestinal bacteria ferment water-soluble fibers, a great deal of intestinal gas may be produced in individuals not accustomed to a high fiber diet, leading to flatulence and abdominal discomfort.